In dry etch processes for semiconductor wafers, wafer surface temperature is a critical process parameter. Even minor fluctuations in wafer temperature during processing can effect the characteristics of the etched wafer, such as etch rate, taper angle of etched features, and sidewall deposition rate. Accordingly, it is desirable to provide local temperature uniformity during such processing. One method of temperature control during processing is obtained by feeding a fluid from a reservoir through a feeding line built within a chuck on which the wafer is suspended during processing. The temperature of the fluid is measured and controlled in the reservoir and is pumped through the chuck. Accordingly, the temperature of the chuck surface is determined by the set temperature of the reservoir and isolation losses in the coolant lines. However, this method for controlling temperature is very limited. For example, different temperatures across the chuck surface cannot be compensated for or controlled. In fact, this problem escalates as the wafer diameter increases. Furthermore, this method has a very long response time (approximately 2 minutes per degree).
Another method of controlling temperature during processing is obtained by improving the heat transfer characteristics between the wafer and the chuck through backfilling (introducing helium or a similar gas into the interstices between the wafer and a susceptor to increase the heat exchanging rate between them). This procedure is described in detail in U.S. Pat. No. 5,270,266 to Hirano et at., issued on Dec. 14, 1993. Thus, by varying the pressure of the gas introduced, the temperature of the wafer can be moderately controlled.
However, methods of controlling wafer temperature by locally applying different pressures via Helium backfilling is limited to simple geometries (center versus edge). Additionally, such methods are restricted to electrostatic chucks only.
A further method of controlling wafer temperature during processing is to fabricate a thermoelectric device having an array of thermocouples which operate using the Peltier effect (the absorption of heat at a junction through which an electric current flows). For example, U.S. Pat. No. 4,493,939 to Blaske et al., issued on Jan. 15, 1985, discloses a method and apparatus for manufacturing a thermoelectric device comprising a matrix member which is fabricated from an array of thermoelectric elements. However, this patent does not indicate how to use the described array of thermoelectric elements in conjunction with a wafer for controlling the temperature of the wafer.
Accordingly, it is the object of the present invention to substantially overcome or eliminate such disadvantages by providing an apparatus for sensing and controlling the local temperature distribution of a semiconductor wafer during processing that is quicker in response time and provides superior localized temperature control as compared to those of the prior art.